Pregnancy a risk factor for kidney stone

Pregnancy carries an increased risk for developing a first-time symptomatic kidney stone, which is highest close to delivery and then reduced by first year postpartum, although a modest risk increase is retained beyond 1 year, according to a study.

The population-based matched case-control study looked at women residing in Olmsted County, Minnesota, US. A total of 945 first-time symptomatic kidney stone formers aged 15-45 years and 1,890 age-matched controls participated. The index date was defined as the date of onset of a symptomatic kidney stone for both the case and matched controls.

Compared with those who were not pregnant, women in their first trimester of pregnancy were not at higher risk of developing a symptomatic kidney stone (odds ratio [OR], 0.92; p=0.8). But the risk rose by twofold during the second trimester (OR, 2.00; p=0.007) and further by 2.7 times during the third trimester (OR, 2.69; p=0.001).

Of note, the risk increase peaked at 0 to 3 months after delivery (OR, 3.53; p<0.001) before returning to baseline by 1 year after delivery.

The observed associations persisted despite controlling for confounding factors, such as age and race, diabetes mellitus, hypertension, and obesity. Age, race, time period, or number of prior pregnancies had a null effect on the risk of a first-time symptomatic kidney stone.

However, having a prior pregnancy (delivery date >1 year ago) was also associated with a first-time symptomatic kidney stone (OR, 1.27; p=0.01).

The study was limited by its observational design and the inclusion of a predominantly White population. Additionally, the exact timing of stone formation could not be determined.